Twin fluke anchor



June l, 1943. R. s, DANFRTH 2,320,966

TWIN FLUKE ANCHOR Original Filed March 13, 1939 ATTQRNEIY l Glclllncu dullc I., LIJ

plauto UNITED STATES PATENT OFFICE Original application March 13, 1939, Serial No. 261,617. Divided and this application April 1, 1941, Serial No. 386,387

14 Claims.

This is a division of my application Serial Number 261,617 filed March 13, 1939, now abandoned.

The invention relates to anchors for mooring floating vessels and more particularly to forms adapted for use by yachts, fishing boats and other small craft, though not limited thereto.

The invention relates particularly to that specie type of anchor commonly referred to as the navy type. Such an anchor consists essentially of a shank, two fluke arms, a corresponding number of flukes attached to or formed on the arms, and a stock arranged in a plane parallel to the plane of the uke arms and located at the forward or after end of the shank, a ring or opening for the attachment of the chain or cable being provided.

My invention relates to the discovery of certain critical angular relations between the ukes of the anchor and its shank, by which the digging and holding power of an anchor of this type are very strongly influenced. The invention concerns also certain relations of contour, width, and spacing of flukes, and the forms of certain parts, by which both resistance to digging in and tendency to rotate, both of which normally tend to reduce the holding power and the dependability of an anchor of this type, are substantially elimmated.

The objects of the invention are to provide an .certainty of operation, freedom from risk of fouling, and other advantages herein disclosed.

This combination of elements takes the form herein in which a pair of flukes having their faces `arranged in the same plane swivel freely in the after end of the shank and are limited as to the extent of the swivelling movement by suitable stop means, the ukes thus coming automatically to engaging position by gravitation.

In the attached drawing:

Figure l is a diagram illustrating and naming the various' angles to which reference is hereinafter made, used in discussing the invention.

Figure 2 is a plan view of my improved navy type anchor; a portion of the crown is cut away to show the attachment and pivotal mounting of the flukes.

Figure 3 is a side elevation of the same, showing the fluke arm and fluke in the extended or oper-v ating position; a portion of the stock and crown .are cut away to illustrate the construction.

Figure 4 is a section taken through the stock and crown.

Referring rst to Figure 1, which is to be considered strictly as a diagram: I represents the shank of the anchor; l2 a fluke arm, or any one of them if the anchor has more than one fluke; I I is the fluke which is xed to the arm, and I3 is the point of cable attachment. The line A-B is the axis of the shank; the line C-D is parallel to the longitudinal face of the fluke (in the diagram it is also the axis of the fluke arm, but this is immaterial as the arm need not be aligned with the fluke face but may be of any preferred form) E is a point on each fluke face located at the center of area of the face; F is the point of the fiukes; G is the point of intersection of lines A-B and C-D. The line H-I represents a plane passed through the point of cable attachment and the point of the flukes; the line J-K represents a plane passed through the areal center (E) of each iluke and the point of cable attachment. If the diagram is taken to represent an anchor in which the fluke arms fold or swivel., it is assumed that the arm and flukes are at the outward limit of travel.

Using these conventions, the angle A-G-C between the face of the uke and the axis of the shank is termed fluke angle.

The angle D-F-I between the fluke faces and the plane passed through the fluke points and the point of cable attachment is termed point angle.

The angle D-E-K between the fluke faces and the plane passed through the areal centers of the flukes and the point of lcable attachment is termed attack angle.

These three terms are used in the sense here dened throughout the specification and the claims.

The fluke angle is xed in the construction of the anchor, as by the positioning of the stops in a swivelling or folding type. The width of this angle affects the length of shank which must be provided in order to obtain desired point and attack angles.

Ordinarily this angle should not be less than 20 nor more than 35, and a mean angle of 25 is suitable for most purposes. This angle does not affect the functioning of the anchor except as its value affects the point and attack angles or the length of the nuke arms for any given length of shank.

The point angle is controlled by the fluke angle, the length of the shank and the length of the fluke and arm as measured to the tip of the fluke. The point angle may be decreasedwithout changing the attack angle by so modifying the shape of the flukes as to lower their center of area. The Width of this angle should be less than to ensure prompt and certain initial engagement of the flukes with relatively hard ground, and I prefer to use a point angle of about 57. Point angles as high as even 80 may be used but with less reliable performance. An angle of is consider-ed as within the range of 60 to 80, this angle being generally satisfactory except in extremely hard holding ground.

The attack angle is of the rst importance as regards holding power, the ability of the anchor to dig in and bury itself deeply, and the ability to remain buried and thus tomaintain its holding power even when dragged for considerable distances.

As the result of numerous experiments I have discovered that the optimum Value for the attack angle in average holding ground is approximately 37; that when this width of angle is materially exceeded there is less certainty of the anchor digging in to afford its optimum holding power, and that as the angle is decreased below about 37 the holding power is reduced slowly and at a declining rate and drops to about one-half the optimum rate at about One objection to the more abrupt angle of attack is the decrease in reliability of holding occasioned by its use. As the attack angle increases, there is increasing liability of the face of the ilukes becoming shod with holding ground material. On clay bottoms particularly, and with the wider attack angles, a prism or pyramid of ground material is likely to form and remain on the advancing faces of the nukes, and when this occurs the flukes rise out of the ground and the anchor drags with practically no holding power.

At the preferred attack angle of 37, or at a less angle, the ground through which the anchor drags in taking hold flows over the face of the fluke, eliminating the possibility of the flukes becoming shod and urging them downwardly until further burying movement is stopped by increasing resistance offered by the shank or by the flukes coming to a position in which their faces are parallel to the plane in which the forward end of the anchor is being moved by the dragging strain.

Another objection to a Wide attack angle is found in the decrease in downwardly acting force tending to bury the anchor as the angle becomes more abrupt. An anchor drags in taking hold, and digging in is due to the downward force exercised by the ground flowing over the forward faces of the flukes, this force decreasing as the angle becomes more abrupt. The holding ground is ordinarily harder and more resistant at depth than immediately on its surface. The result of these two factors is that an anchor having an attack angle as wide as 45 will often or usually bury only the ukes and will drag in that position, with relatively slight holding power, while an anchor with an attack angle of 37 or less will, if of the proper form, bury itself completely, leaving only the forward end of the shank above the ground surface.

The critical point in the progress of an anchors burying itself occurs when the portion of the anchor aft of the nukes (as for example, a fluke arm arranged at an angle to the fluke, the head or housing surrounding the pivot point in a navy anchor, or a stock located at the after end) encounters the surface of the ground. As the anchor swings downwardly, the angle of the fluke to the direction of dragging becomes constantly less and the downward component of the dragging force consequently increases. If

these resisting elements can once be carried below the surface, the force which will accomplish this will continue to carry them downward and permit the anchor to bury.

For this reason the point of rst encounter of a resisting element with the ground should be located as far as possible aft of and above the center of area of the fluke faces, and an anchor in which the flukes and fluke arms are substantially axially aligned (as in Figure 3, for example) of one in which the flukes themselves extend back to the pivot point, will tolerate a materially wider attack angle than a form in which the fluke arms are formed at an angle to the face of the flukes. In the form of Figure 3 and its equivalents, an attack angle as wide as 50 may often be used to advantage, greater holding power being gained at the cost of some decrease in reliability of digging in.

Further, in certain types of anchors having the after end so formed as to offer a relatively slight resistance to downward movement into the holding ground, it may be permissible to use an attack angle as high as 50. A form of anchor adapted to this higher attack angle is illustrated in Figure 2. In adopting this higher angle of attack the reliability of engagement is diminished and the risk of becoming shod is increased, but the depth to which the after end of the anchor Will bury itself under favorable conditions is also increased, this depth being limited by the angle of the shank to the surface of the holding ground when the flukes have assumed a position parallel to the surface. Any lateral projection from the after end of the anchor of such form and dimensions as seriously to resist burial, such for example as fluke arms projected at right angles or the use of a stabilizing bar or stock of excessive longitudinal area or of angular cross section at the after end of the anchor, will inhibit the use of the wider attack angle and is undesirable at any angle.

The reduced holding power at less than the optimum angle is due to the reduction in effective area of flukes as the attack angle diminishes. For a fluke of any given area and regardless of contour, the effective area of the uke is to its actual area in the relation of the height F-M of the triangle L--M-F bears to the hypotenuse F-L. For the four angles here considered, and taking the actual area of the fluke at the effective areas are: at 50=76.6%; at 45=70.7%; at 37=60.2%; and at 20=34.2%. Or taking the effective area at 37 as 100% the relations are: at 50=126.5%; at 45=116.9%; at 37=100.0%; and at 20=56.6%. These relations are independent of the contour of the fluke face.

By reason of the limitations above stated, I consider that the limits of actual utility for the attack angle may be xed at 20 and at 43 where no limitation is placed on the type of anchor, and at 20 to 50 in the types in which the burial resistance is reduced to the minimum, while about 37 is the optimum value for all types in the average holding ground which the anchor is liable to encounter.

A specific structure in which I prefer to incorporate the basic principles of the invention as well as certain novel features of structure is shown in Figures 2, 3 and 4 of the attached drawing. Referring to these gures, which represent a twin-fluke pivoted or so-called navy type anchor; I0 is the shank; lI-II are twin flukes fixed in a common plane by attachment to fluke arms I2-l2 which in turn are attached to or integral with a housing i4. The housing is cored out as at I5 to allow the after end of the shank to enter it. The length of the fiukes may, if preferred, be such as to eliminate the fluke arms I2, the flukes being pivotally attached directly to the housing. The point of cable attachment at the forward end of the shank is indicated at I3.

A stock I6 is passed through holes bored in the sides of the housing and the after end of the shank and acts at once as a stabilizing bar and-a pivot pin. This stock is provided with two small projections Il and IB, spaced to engage the outer faces of the housing. One of these projections I8 passes through a slot I9 in the housing and shank and, after it is in position and turned, a plug 20 threaded into the housing is inserted to prevent the projection from again aligning with the hole and allowing the stock to slip out.

The swivelling motion of the arms and i'lukes around the after end of the shank is limitedby the engagement of the internal faces 2I--2I of the housing with the upper and lower faces of the shank.

In anchors of the free swivelling type it is necessary to lift the after end of the shank a short distance above the ground in order to allow the uke to gravitate down to the slight initial angle which will cause it to engage and to swivel into operative position. For this purpose I provide a small upward and downward extension of the housing, as at 22-22, which may be cored out as at 23 to reduce its ground resistance as far as possible. This extension is usually termed crown and will be so designated here and in the claims.

In order to prevent the anchor from lying or turning on its side, in which position it is .inoperative, it is necessary to provide it with a stock or some equivalent therefor. In the older forms of anchor this stock is passed through the forward end of the shank, but in order to ensure positive initial engagement and also to permit the anchor to be hauled into the hawse-pipe, I usually place it at the after end of the anchor. The stock or stabilizing bar can take various forms for, as I have indicated, its purpose is to prevent the anchor lying or turning on its side. The term stock as used here and in the claims is broadly applied to the means for 1) ensuring positive initial engagement and (2) `preventing undesirable rotation of the anchor about the shank axis.

In this after position certain characteristics of the stock which, when it is placed at the forward end are largely matters of indifference, be- I come important or even critical.

First, the length of the stock should be such that its end lies outside a line projected rearwardly from the outer forward edge of the fluke (the line S-T of Figure 2) or, if the fluke is outwardly curved, a line struck through the point of the fluke and a point located on the outer fluke edge one-fourth the Juke length aft of the fluke point. This rearwardly projected line is referred to in the claims as the projected fluke edge. If the end of the stock falls within this line, i. e., on the side toward the shank, the anchor is liable to ride on the side of the uke and the tip of the stock and fail to engage.

Next, anchors of the type shown in Figures 2 to 4 depend almost entirely on their angular relations for digging in, rather than on their weight, and in turn depend for their holding power on the extent to which they bury themselves. The stock located at the after end of the shank resists digging in, to an extent which depends in part on its form in cross section but to a much greater extent on its longitudinal sectional area, as measured in a plane normal to the plane of the forward uke face when the anchor is in operative position but excluding that portion included in the crown area as hereinafter described. For this reason the longitudinal sectional area of the stock, measured as defined above, and termed longitudinal stock area" herein and in the claims, should be as small as is consistent with stiffness. I have determined that the longitudinal sectional area of the stock, measured from tip to tip, should not exceed the total fluke face area, and I prefer to keep the stock area as low as one-half or one-quarter of the fluke face area.

In referring to fluke faces areas, it will be understood that I refer only to the advancing face of the fluke or flukes which may be in -the ground in any one position of the anchor. I n a twin fluke or navy anchor this will be the forward faces of the twin flukes.

Finally, the stock may, if improperly formed, tend strongly to rotate the anchor about its shank. This tendency may be so strong as practically to destroy the usefulness of the anchor if the stock is of angular or irregular cross section, as in such case the forces tending to produce rotation are unbalanced if the stock, in digging in, encounters unequal ground resistance at the two sides of the shank. For this reason I use a stock preferably of circular cross section, cylindrical or gently tapering, though results not quite so good may be had with a stock having arcuate leading and trailing faces but not strictly circular.

In addition to lforming the stock in the manner described, the after end of the anchor, and particularly the butt or housing around the pivotal point in any swivelling type anchor including that portion usually termed the crown, should be rounded so far as possible and should be of the smallest dimensions consistent with strength in order to minimize resistance to digging in. In anchors of the navy type, the ratio of cross sectional area to fluke area should not exceed one to three and is preferably of the order of one to six. This area, termed crown area hereinafter and in the claims is the maximum vertical cross-sectional area. conned by 'the boundaries of the after portion or crown of the anchor in a plane normal to the shank axis when the shank and Yflukes are horizontal, disregarding that portion of the stock extending beyond the crown but including that portion passing through or within the crown.

I have previously indicated that the longitudinal sectional area of the stock, measured from tip to tip, in a plane normal to the plane of forward fluke faces when the anchor is in operative position, should not exceed the total uke face area and that I--preferred to keep the stock area as low as a quarter` of the fluke face area. iently combined with the crown area as a single criterion. This is only logical treatment of these values for, with the stock at the after end, their combined areas provide the major resistance to be overcome if the anchor is to bury itself under continued pull. The minimum values of the ratios are a fluke area to crown area ratio of three to one and a fluke area to stock area ratio of one to one. This corresponds to a combined ratio of three to four; or the total fluke area divided by the sum of the stock area and the crown area should be 0.75

For simplicity, this criterionis convenwith alternative higher values of 0.86 and 1.2.

As the effectiveness of any unbalanced, more or less vertically applied force in producing rotation increases with the distance from the point of application of the force to the axis of the shank, the relative dimension of the twin flukes of a navy anchor, and their spacing from the shank are of considerable importance. For this reason the lateral dimensions of the anchor should be reduced as far as is consistent with proper clearance between the flukes and the shank, with obtaining the necessary fluke area, and with maintaining the desired angular relations Within the limits above fixed.

Thus, the spacing N (Figure 2) of the point of each nuke from the axis of the shank should not exceed one-fteenth of the length O of the shank, when the end of the stock falls within (i. e., on the shank side of) the projected fluke edge, but may be as much as one-eighth of the shank length when the end of the stock extends beyond this projected line for a distance not less than onefourth the total length of the half stock, measured from tip to shank axis. The shank length, as is shown in Figure 2, is the distance from the point of cable attachment to the center of the pivot; and, as so defined, this term is used herein and in the claims.

The distance P from the center of area Q of each fluke to the axis of the shank should not exceed one-thirteenth of the shank length O when the tip of the stock falls within the line S-T, but may be as great as one-sixth when the stock projects over this line for a distance not less than one-fourth the length of the half stock. In other words, the distance between the centers of areas Q (that is, the value 2P) should not exceed one over 6.5 or 15.4% of the shank length when the tip of the stock falls within the line S-T. It can be as great as a third of the stock length when the stock extends beyond the line S--T.

The distance R from the outermost point of the fluke to the axis of the shank should preferably be about one-seventh of the shank length, but may be as much as one-fourth the shank length when the stock projects over the line S-T a distance not less than one-fourth the length of the half stock.

All of these limitations as to lateral spacing apply to navy type anchors having the stock located at the after end of the shank.

Whether the stock be placed at the after end of the navy type anchor, as shown, or at the forward end, as is conventional, no laterally projecting portion of the anchor other than the stock should extend from the axis of the shank a distance greater than one-fourth the length O of the shank, and if the stock is placed at the after end, it is further necessary that the total sectional area of all parts projecting from the shank a distance greater than one-fourth the shank length, said area being measured in planes parallel to the plane of the iiuke, should not exceed one-half the combined area of the forward faces of the twin ukes. With the stock at the forward end of the shank the point spacing N from the shank axis should not exceed one-eighth the shank length; the center of area spacing P should not exceed one-sixth the shank length, and the outermost point spacing R should not exceed onefourth the shank length.

The twin nukes should, of course, be practically identical in area and contour and the outer edges should preferably be beveled as at 25 in Figure 2.

The forward faces of the flukes should be free from ribs or other obstructions to the free iiow of the ground material over them. Even longitudinally extending ribs, if of material height, strongly increase the tendency for the iluke to become shod and thus ineifective. The two lukes, being xed in a common plane, function as one and should be considered as a single twin fluke.

By keeping within the limits of dimensions above recited I produce a navy type anchor which is substantially free from any tendency to rotate and which has the maximum digging in ability and the maximum holding power for any given uke area. The results of the following tests show the advantages of such an anchor.

The tests of which the results are recited below were made with four anchors, all except the kedge having identical fluke areas, all of the tests being made on the same holding ground and under identical conditions. Each test was several times repeated and the figures given are the limit tensions maintained while the anchors were being dragged. The anchors tested were:

No. 1, a conventional kedge type anchor, Weight pounds, fluke angle 54, attack angle 76.

No. 2, a commercial light weight folding anchor having the flukes spaced from the shank by laterally projected arms, weight 20 pounds, fluke angle 271, attack angle 45.

No. 4, a navy type anchor as herein described (Figures 2, 3 and 4), weight 27 pounds, nuke angle 25, attack angle 37,

The holding power results obtained were in the following ranges:

Anchor No. 1 dug in until its fluke was buried and dragged in that position. Anchor No. 2 dug in until the stock, which was of angular cross section and of rather large area, was somewhat above the ground surface, and dragged in that position. Anchor No. 4 buried itself completely except for a small portion of the forward end of the shank, and remained at that depth consistently even when dragged considerable distances.

The application of the optimum point and attack angles to other than the navy type of anchor produces highly benecial results, though the benet is to some extent offset by undesirable features of structure which are reilected both in holding power and in inconvenience of form.

A highly desirable feature of the navy type of anchor referred to is complete absence of risk of the anchor fouling the cable as the vessel ranges with wind or current. This risk is intrinsic in all forms having two flukes, one of which must project above the ground at all times.

The invention shown and described herein is clearly differentiated by each of the appended claims from that invention claimed in my Patent No. 2,249,546.

Having set forth herein only the preferred form of twin uke anchor of my invention it is to be understood that various modications thereof can be made by those skilled in the art without departing from my invention as denned in the claims.

To particularly point out and distinctly claim the part, improvement, or combination which I.

claim as my invention I include each of the following claims:

1. An anchor of the twin nuke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of nukes, a crown adjacent the after end of said nukes having ground engaging portions thereon raised above the plane of the nuke faces to lift said shank after end oif the ground and thereby rotate the nukes to engage the ground, and a pivot mounting said nukes on said shank at said after end with said nukes extending toward said forward end and with said shank between said nukes, said nukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and nukes being so proportioned and positioned relative to each other when in operative position that (1) a plane passed through said point of cable attachment and through the centers of area of the nuke forward faces makes an angle with the plane of the forward nuke faces in the range of 20 to 50, and 2) a plane passed through said cable attachment point and the forward ends of said nukes in operative position makes an angle with the projected nuke forward faces of less than 75, the combined area of said nuke forward faces having a ratio to the sum of the longitudinal stock area and crown area, both as herein denned, greater than 0.86 to 1, said stock projecting on each side of said shank beyond a line drawn through the point of each nuke and a second point located on the outer edge of said nuke one-fourth of the nuke length aft from the point of said nuke, the total horizontal sectional area of those portions of said anchor spaced from said shank a distance greater than one fourth the shank length measured at a right angle from the longitudinal axis thereof when the nukes are lying horizontally and in the plane of the shank and on both sides thereof being less than half of the area of the nuke forward faces.

2. An anchor of the twin nuke type comprising a shank having a forward and an after end t with a point of cable attachment at said forward end, a stock at said after end, a pair of nukes, acrown at the after end of said nukes having ground engaging portions thereon raised above the nuke faces to slide along the ground and engage the nukes with the ground when the anchor is on the ground with the nukes and shank in substantially the same plane, and a pivot mounting said nukes on said shank at said after end with said nukes extending toward said forward end and with said shank between said nukes, said nukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and nukes being so proportioned and positioned relative to each other when in operative position that (1) a plane passed through said point of cable attachment and through the centers of area of the nuke forward faces makes an angle with the plane of the forward-nuke faces in the range of 20 to 43, 2) a plane passed through said cable attachment point and the forward ends of said nukes in operative position makes an angle with the projected nuke forward faces of approximately 57, the centers of area of said nuke forward faces being spaced apart a distance less than one-third of the length of the shank, the combined area of said nuke forward faces having a ratio to the sum of the longitudinal stock area and crown area, both as herein denned, greater than 0.75 to 1.

3. An anchor of the twin nuke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of nukes each having a major forward portion thereof substantially triangular in outline, a crown adjacent the after end of said nukes having ground engaging portions thereon raised above the plane of the nuke faces to lift said shank after end off the ground and thereby rotate the nukes to engage the ground, and a pivot mounting said nukes on said shank at said after end with said shank between said nukes, said nukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and nukes being so proportioned and positioned relative to each other when in operative position that the plane of the forward nuke faces makes an angle in the range of 20 to 35 to said shank, the combined area of said nuke forward faces having a ratio to the sum of the longitudinal stock area and crown area, as herein denned, greater than 0.75 to 1.

4. An anchor of the twin nuke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of nukes, a crown adjacent the after end of said nukes having ground engaging portions thereon raised above the plane of the nuke faces to lift said shank after end off the ground and thereby rotate the nukes to engage the ground, and a pivot mounting said nukes on said shank at said after end with said nukes extending toward said forward end and with said shank between said nukes, said nukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and nukes being so proportioned and positioned relative to each other when in operative position that (1) a plane passed through said point of cable attachment and through the centers of area of the nuke forward faces makes an angle with the plane of the forward nuke faces in the range of 20 to 50, and (2) a plane passed through said cable attachment point and the forward ends of said nukes in operative position makes an angle with the projected nuke forward faces of less than 75, the combined area of said nuke forward f faces having a ratio to the sum of the longitudinal stock area and crown area, as herein denned, greater than 0.75 to 1.

5. An anchor of the twin nuke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of nukes each having a major forward portion thereof substantially triangular in outline, a vcrown at the after end of said nukes having ground engaging portions thereon raised above the nuke faces to slide along the ground and engage the nukes with the ground when the anchor is on the ground with the nukes and shank in substantially the same plane, and a pivot mounting said nukes on said shank at said after end with said nukes eX- tending toward said forward end and with said shank between said nukes, said nukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and nukes being so proportioned and positioned relative to each other when in operative position that a plane passed through said cable attachment point and the forward ends of said iiukes in operative position makes an angle with the projected fiuke forward faces of less than 75, the centers of area of said fluke forward faces being spaced apart a distance less than one-third of the length of the shank, the combined area of said fiuke forward faces having a ratio to the sum of the longitudinal stock area and crown area, as herein defined, greater than 0.75 to 1.

6. An anchor of the twin fluke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a pair of iiukes, and a crown at the after end of said flukes having ground engaging portions thereon raised above the fluke faces to slide along the ground and engage the flukes with the ground when the anchor is on the ground with the flukes and shank in substantially the same plane, and a pivot mounting said flukes on said shank at said after end with said flukes extending toward said forward end and with said shank between said ukes, said flukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and flukes being so proportioned and positioned relative to each other when in operative position that (1) the plane of the fluke forward faces makes an angle with the shank in the range of 20 to 35, and (2) a plane passed through said cable attachment point and the forward ends of said flukes in operative position makes an angle with the projected fiuke forward faces of less than 75, the combined area of said fluke forward faces having a ratio to the sum of the longitudinal stock area and crown area, both as herein defined, greater than 0.86 to 1, the centers of area of said fluke forward faces being spaced apart a distance less than one-third of the length of the shank.

7. An anchor of the twin fluke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of flukes, a crown adjacent the after end of said flukes having ground engaging portions thereon raised above the plane of the fluke faces to lift said shank after end off the ground and thereby rotate the fiukes to engage the ground, and a pivot mounting said flukes on said shank at said after end with said flukes extending toward said forward end and with said shank between said flukes, said flukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and ukes being so proportioned and positioned relative to each other when in operative position that (1) a plane passed through said point of cable attachment and through the centers of area of the fluke forward faces makes an angle with the plane of the forward fluke faces in the range of 20 to 50, and (2) a plane passed through said cable attachment point and the forward ends of said flukes in operative position makes an angle with the projected fiuke forward faces of less than 75, the combined area of said iiuke forward faces having a ratio to the sum of the longitudinal stock area and crown area, as herein defined, greater than 0.75 to 1, the centers of area of said fluke forward faces being spaced apart a distance less than one-third of the length of the shank.

8. An anchor of the twin fluke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of fiukes, a crown adjacent the after end of said flukes having ground engaging portions thereon raised above the plane of the fluke faces to lift said shank after end off the ground and thereby rotate the flukes to engage the ground, and a pivot mounting said flukes on said shank at said after end with said fiukes extending toward said forward end and with said shank between said ukes, said fiukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and flukes being so proportioned and positioned relative to each other when in operative position that (l) a plane passed through said point of cable attachment and through the centers of area of the iiuke forward faces makes an angle with the plane of the forward fluke faces of approximately 37, and (2) a plane passed through said cable attachment point and the forward ends of said flukes in operative position makes an angle with the projected fluke forward faces of approximately 57, the combined area of said fluke forward faces having a ratio to the sum of the longitudinal stock area and crown area, as herein defined, greater than 0.75 to 1, said stock projecting on each side of said shank beyond a line drawn through the point of each fiuke and a second point located on the outer edge of said fiuke one-fourth of the fluke length aft of the point of said uke.

9. An anchor of the twin fluke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of flukes, a pivot mounting said flukes on said shank at said after end with said flukes extending toward said forward end and with said shank between said fiukes, said iiukes simultaneously engaging the ground in a substantially common plane when in operative position, and a crown at the after end of said flukes having ground engaging portions thereon sloping rearwardly away from the flukes at an acute angle to the plane of the ukes and raised above the -iiuke faces to slide along the ground and engage the flukes with the ground when the anchor is on the ground with the ukes and shank in substantially the same plane, the combined area of the iiuke forward faces having a ratio to the sum of the longitudinal stock area and crown area, as herein defined, greater than 0.75 to 1.

10. An anchor of the twin iiuke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of flukes, a crown adjacent the after end of said flukes having ground engaging portions thereon raised above the plane of the iiuke faces to lift said shank after end off the ground and thereby rotate the flukes to engage the ground, and a pivot mounting said flukes on said shank at said after end with said iiukes extending toward said forward end and with said shank between said fiukes, said flukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and flukes being so proportioned and positioned relative to each other when in operative position that (1) a plane passed through said point of cable attachment and through the centers of area. of the uke forward faces makes an angle with the plane of the forward fluke faces in the range of 20 to 50, and (2) a plane passed through said cable attachment point and the forward ends of said flukes in operative position makes an angle with the projected fiuke forward faces of less than 75, the combined area of said fluke forward faces having a ratio to the sum of the longitudinal stock area and crown area, both as herein defined, greater than 0.75 to 1, said stock projecting on each side of said shank beyond a line drawn through the point of said fluke and a second point located on the outer edge of said fluke one-fourth of the fluke length aft from the point of said fluke.

11. An anchor of the twin fluke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of flukes, a crown adjacent the after end of said iiukes having ground engaging portions thereon raised above the plane of the fluke faces to lift said shank after end off the ground and thereby rotate the ukes to engage the ground, and a pivot mounting said ukes on said shank at said after end with said flukes extending toward said forward end and with said shank between said flukes, said flukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and flukes being so proportioned and positioned that a plane passed through said cable attachment point and the forward ends of said fiukes in operative position makes an angle with the projected uke forward faces of less than 75, the combined area of said fluke forward faces having a ratio to the sum of the longitudinal stock area and crown area, as herein dened, greater than 0.75 to 1, said stock projecting on each side of said shank and beyond a line drawn through the point of said fluke and a second point located on the outer edge of said fluke one-fourth of the fluke length aft of the point of said fluke.

12. An anchor of the twin uke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock, a pair of flukes, a crown adjacent the after end of said nukes having ground engaging portions thereon raised above the plane of the fluke faces to lift said shank after end off the ground and thereby rotate the flukes to engage the ground, and a pivot mounting said flukes on said shank at said after end with said flukes extending toward said forward end and with said shank between said flukes, said fiukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and ukes being so proportioned and positioned relative to each other when in operative position that (l) a plane passed through said point of cable attachment and through the centers of area of the fiuke forward faces makes an angle with the plane of the forward fluke faces in the range of to 50, and (2) a plane passed through said cable attachment point and the forward ends of said ilukes in operative position makes an angle with the projected :duke forward faces of less than 75, the combined area of said fluke forward faces having a ratio to the sum of the longitudinal stock area and crown area, as herein defined, greater than 0.75 to 1, the centers of area of said fluke forward faces being spaced apart a distance less than one-third of the length of the shank.

13. An anchor of the twin fiuke type compris- Cil ing a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of ukes,

' a crown at the after end of said ukes having ground engaging portions thereof sloping rearwardly away from the fiukes at an acute angle to the plane of the ukes and raised above the fluke faces to slide along the ground and engage the flukes with the ground when the anchor is on the ground with the flukes and shank in substantially the same plane, a pivot mounting said flukes on said shank at said after end With said flukes extending toward said forward end and with said shank between said flukes, said flukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and nukes being so proportioned and positioned relative to each other when in operative position that (1) a plane passed through said point of cable attachment and through the centers of area of the uke forward faces makes an angle with the plane of the forward fluke faces in the range of 20 to 50 and (2) a plane passed through said cable attachment point and the forward ends of said flukes in operative position makes an angle with the projected fluke forward faces of less than the combined area of said fluke forward -faces having a ratio to the sum of the longitudinal stock area and crown area, as herein dened, greater than 1.2 to 1, said stock projecting beyond a line drawn through the point of the fluke and a second point located on the outer fluke edge one-fourth of the fluke length aft from the fluke point, the total horizontal sectional area of those portions of said anchor spaced from said shank a distance greater than one fourth the shank length measured at a right angle from the longitudinal axis thereof when the ilukes are lying horizontally and in the plane of the shank and on both sides thereof being less than half of the area of the fluke forward faces.

14. An anchor of the twin fluke type comprising a shank having a forward and an after end with a point of cable attachment at said forward end, a stock at said after end, a pair of flukes, a

crown adjacent the after end of said fiukes having ground engaging portions thereon 'raised above the plane of the fluke faces to lift said shank after end off the ground and thereby rotate the flukes to engage the ground, and a pivot mounting said flukes on said shank at said after end with saidflukes extending toward said forward end and with said shank between said fiukes, said fiukes simultaneously engaging the ground in a substantially common plane when in operative position, said shank and flukes being so proportioned and positioned relative to each other when in operative position that (1) a plane passed through said point of cable attachment and through the centers of area of the fiuke forward faces makes an angle with the plane of the forward fluke faces in the range of 20 to 50, the longitudinal area of said stock being not more than one half of the area of the fluke forward faces and the area of the crown being not more than one third of the area of said fiuke forward faces, said stock projecting on each side of said shank and beyond a line drawn through the point of the fluke and a second point located on the outer edge of said fiuke one-fourth of the fiuke length aft from the point of said fluke.

RICHARD S. DANFORTH. 

